القواذف الإلكترونية وأقطاب الشاشة .. كتاب التلفزيون الملون والعادي

11-4 Electronic launchers and screen electrodes:

They are three launchers in the color screen - and each launcher emits an electronic beam that passes through the holes in the mask - to incite a point of light of red, green or blue color and pass through the same hole the three rays at one moment, each beam scanning its own phosphorescent points, which represent 1/3 of the total number For screen points that generate one of the three colors.

The three launchers are located in the screen valve in one of the following two forms:
1 - Delta method - the launchers are in the form of the vertices of an equilateral triangle. The phosphorous triplets on the screen are also in the form of a triangle (11-12).

2- The line method - so the launchers are on one line (in line). The phosphorous dots on the screen are also on one line - Figure (11-13). Each electronic gun (launcher) contains the following electrodes: and the figure
(11-11) and (11-14) explain the poles and their distribution, which are:

1- The heating wick (the heater).

2- The runway.

3- The ruling network.

4- The blocking net (acceleration pole).

E - the third network (the focus network).

6- The second pole elevator for acceleration.

Screen electrodes work:

Heating Filament: (Heater) which is three fuses connected in parallel - fed from two specific poles at the base of the screen valve, usually connected to an AC voltage of 6.3 volts, and its current intensity is (600 to 900 milliamps) in most types. Some small mobile devices feed their filaments with a voltage ranging from (2.3 - 9.0 volts) and a current of (80 - 300 mA). 1 - 6) - or otherwise.

2 - Cathode: It is in a cylindrical shape made of nickel metal coated with oxides of barium, calcium and strontium, which emits electrons from us. Heat it with the heat of the wick.

3 - Control Grid: It is in the form of a closed cylinder with a small hole in its center, which allows the electronic beam to pass towards the screen, and controls the intensity of the beam, and its voltage ranges from zero to 150 volts. By changing the potential difference between the governing grid and the cathode, the beam intensity changes. Thus, the electronic beam is controlled by changing the voltage of the governing network or the cathode voltage or both. The intensity of the beam affects the mixing ratio to obtain correct colors in the colored phosphorescent points. 4- Screening grid: It represents the first anode of the valve and is connected to a direct current ranging from (200) volts to +500 volts. It attracts the beam and accelerates it towards the screen.
E - the third network, the focus pole:

It works to focus the beam, and it represents the work of the optical focus lens - it makes the beam with a small diameter, and this pole is fed with a continuous voltage (from 4 to AH kilovolt).

The final elevator: It is the most important element in giving the beam its final velocity, and its voltage is (from 22) to 32 kV, according to the size of the screen, and its maximum current is (2000) microamps. The most common types are approx
(25 kV) is generated in the high voltage transformer, then the three-voltage multiplier circuit (Cascade), the rectifier and feeds the screen by a cable with strong and thick insulation to a gap in the back wall of the screen connected to the final lift of the screen. A capacitor with a value of (1500) pF is formed between the inner and outer grounded layer in the back of the screen valve. It acts as a smoothing capacitor for the voltage feeding the screen elevator after rectifying it. This capacitor remains charged with high voltage after the device has been cut off for a long time - and poses a danger to the maintenance and repair technician. Therefore, care must be taken when carrying out adjustment work near high voltage places